More than 90 percent of patients with chronic myelogenous leukemia (CML) carry a chromosomal abnormality, termed bcr-abl, that is important in the pathogenesis of the disease. Identification of this chromosomal abnormality is significant in the initial diagnosis of these patients and in following their course after treatment. Messenger RNA is isolated from their peripheral blood and reverse transcribed, and identification of bcr-abl is done on the cDNA using a nested polymerase chain reaction strategy and specific primers followed by gel electrophoresis. Approximately 70 studies have been performed on patients with CML. This project is completed and has been transferred as a "routine" test to the main hematology laboratory, with the need for approval by the senior staff.